System and method for rebalancing generator rotor in-situ

ABSTRACT

A system for rebalancing a generator rotor includes a temporary bearing shield configured to support a non-drive end of the generator rotor, and a pony motor assembly configured for attachment to a drive end of the generator rotor. The pony motor assembly is configured to rotate the generator rotor during a rebalancing operation. The temporary bearing shield and the pony motor assembly enable the generator rotor to be rotated during an in-situ rebalancing operation.

BACKGROUND OF THE INVENTION

The system and method described herein relates generally to generatorrepair. More specifically, the system and method relates to repairing awind turbine generator in-situ.

At least some known wind turbines include machines for convertingvariable speed mechanical input from blades of the wind turbine intoelectric power that is compliant with an electrical grid. For example,some known wind turbines include a doubly fed induction generator (DFIG)for converting the variable speed mechanical input.

Some known DFIG generator rotors have a floating neutral point. This isfrequently provided by a Wye ring. The Wye ring is typically made from acopper bar and is located at the non-drive end (NDE) of the generator.Due to operational stresses which fatigue the brazed connection betweenthe Wye ring and its rotor connection points (or terminal lugs), crackscan develop which lead to discontinuity. When the first crack occurs,the generator continues to function satisfactorily since the current canstill reach all three rotor connection points. However, if a secondcrack occurs in the Wye ring, at least one part (e.g., one phase) of therotor windings are now disconnected from the floating neutral. Thisresults in severe arcing across one of the cracks, and leads to failureof the insulation around the Wye ring. Eventually, cross-over arcingoccurs between the Wye ring and the phase lead. The wind turbinemonitoring system detects this cross-over arcing condition andrecognizes it as a phase fault, and accordingly shuts the wind turbinedown.

In the past, the only way to repair a cracked Wye ring was to replacethe entire generator. To accomplish this repair, a crane capable oflifting heavy loads (e.g., 10 metric tons) to great heights (e.g., 80meters-100 meters) is required. Cranes of this type are expensive andthe generator replacement operation is costly and time consuming. Inaddition, the wind turbine must be out of service until the newgenerator is installed.

BRIEF DESCRIPTION OF THE INVENTION

In an aspect of the present invention, a system for rebalancing agenerator rotor is provided. The system includes a temporary bearingshield configured to support the non-drive end of the generator rotor. Apony motor assembly is configured for attachment to a drive end of thegenerator rotor. The pony motor assembly is configured to rotate thegenerator rotor during a rebalancing operation. The temporary bearingshield and the pony motor assembly enable the generator rotor to berotated during an in-situ rebalancing operation.

In another aspect of the present invention, a system for rebalancing agenerator rotor includes a temporary bearing shield configured tosupport a non-drive end of the generator rotor. The temporary bearingshield includes a plurality of windows configured to permit access to agenerator rotor fan, and so that balancing weights may be attached tothe generator rotor fan. The temporary bearing shield also includes anaccelerometer configured to detect generator rotor imbalance. A ponymotor assembly is configured for attachment to a drive end of thegenerator rotor, and the pony motor assembly is configured to rotate thegenerator rotor during a rebalancing operation. The temporary bearingshield and the pony motor assembly enable the generator rotor to berotated during an in-situ rebalancing operation.

In yet another aspect of the present invention, a method for rebalancinga generator rotor includes the steps of, attaching a temporary bearingshield to a non-drive end of a generator, attaching a pony motorassembly to a drive-end of the generator, connecting the pony motorassembly to the generator rotor, activating the pony motor assembly torotate the generator rotor, detecting a condition of generator rotorbalance or imbalance, and adding weight to the generator rotor if arotor imbalance condition is detected to correct the rotor imbalance.The method is performed on the generator in-situ.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary wind turbine;

FIG. 2 illustrates a schematic view of a known generator;

FIG. 3 illustrates a perspective view of the non-drive end of agenerator;

FIG. 4 illustrates a perspective view of the non-drive end a generatorwith the bearing shield removed;

FIG. 5 illustrates a perspective view of the non-drive end of agenerator with the rotor fan removed;

FIG. 6 illustrates a schematic view of the rotor end windings connectedto the Wye ring;

FIG. 7 illustrates a schematic view of the rotor after a replacement Wyering has been installed, according to an aspect of the presentinvention.

FIG. 8 illustrates a perspective front view of a temporary bearingshield, according to an aspect of the present invention;

FIG. 9 illustrates a perspective back view of the temporary bearingshield, according to an aspect of the present invention;

FIG. 10 illustrates a perspective view of a pony motor assembly,according to an aspect of the present invention;

FIG. 11 illustrates a perspective view of the pony motor assemblyconnected to the generator rotor input shaft, according to an aspect ofthe present invention;

FIG. 12 illustrates a flow chart of a method for rebalancing a generatorrotor in-situ, according to an aspect of the present invention;

FIG. 13 illustrates a schematic view of the system for in-siturebalancing the generator rotor, according to an aspect of the presentinvention;

FIG. 14 illustrates a flow chart of a method for repairing a rotor of agenerator in a wind turbine, according to an aspect of the presentinvention; and

FIG. 15 is an exploded and perspective view of the connectionarrangement used to connect the replacement Wye ring to the connectionlug, according to an aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

One or more specific aspects/embodiments of the present invention willbe described below. In an effort to provide a concise description ofthese aspects/embodiments, all features of an actual implementation maynot be described in the specification. It should be appreciated that inthe development of any such actual implementation, as in any engineeringor design project, numerous implementation-specific decisions must bemade to achieve the developers' specific goals, such as compliance withmachine-related, system-related and business-related constraints, whichmay vary from one implementation to another. Moreover, it should beappreciated that such a development effort might be complex and timeconsuming, but would nevertheless be a routine undertaking of design,fabrication, and manufacture for those of ordinary skill having thebenefit of this disclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements. Anyexamples of operating parameters and/or environmental conditions are notexclusive of other parameters/conditions of the disclosed embodiments.Additionally, it should be understood that references to “oneembodiment”, “one aspect” or “an embodiment” or “an aspect” of thepresent invention are not intended to be interpreted as excluding theexistence of additional embodiments or aspects that also incorporate therecited features.

FIG. 1 is a schematic view of an exemplary wind turbine 100. In theexemplary embodiment, wind turbine 100 is a horizontal-axis windturbine. Alternatively, wind turbine 100 may be a vertical-axis windturbine. In the exemplary embodiment, wind turbine 100 includes a tower102 extending from and coupled to a supporting surface 104. Tower 102may be coupled to surface 104 with anchor bolts or via a foundationmounting piece (neither shown), for example. A nacelle 106 is coupled totower 102, and a main shaft assembly 108 is coupled to nacelle 106. Mainshaft assembly 108 includes a rotatable hub 110 and a plurality of rotorblades 112 coupled to hub 110. In the exemplary embodiment, main shaftassembly 108 includes three rotor blades 112. Alternatively, main shaftassembly 108 may have any suitable number of rotor blades 112 thatenables wind turbine 100 to function as described herein. Tower 102 mayhave any suitable height and/or construction that enables wind turbine100 to function as described herein.

Rotor blades 112 are spaced about hub 110 to facilitate rotating mainshaft assembly 108, thereby transferring kinetic energy from wind 114into usable mechanical energy, and subsequently, electrical energy. Mainshaft assembly 108 and nacelle 106 are rotated about tower 102 on a yawaxis 116 to control a perspective of rotor blades 112 with respect to adirection of wind 114. Rotor blades 112 are mated to hub 110 by couplinga rotor blade root portion 118 to hub 110 at a plurality of loadtransfer regions 120. Load transfer regions 120 each have a hub loadtransfer region and a rotor blade load transfer region (both not shownin FIG. 1). Loads induced to rotor blades 112 are transferred to hub 110via load transfer regions 120. Each rotor blade 112 also includes arotor blade tip portion 122.

In the exemplary embodiment, rotor blades 112 have a length of betweenapproximately 30 meters (m) (99 feet (ft)) and approximately 120 m (394ft). Alternatively, rotor blades 112 may have any suitable length thatenables wind turbine 100 to function as described herein. For example,rotor blades 112 may have a suitable length less than 30 m or greaterthan 120 m. As wind 114 contacts rotor blade 112, lift forces areinduced to rotor blade 112 and rotation of main shaft assembly 108 aboutan axis of rotation 124 is induced as rotor blade tip portion 122 isaccelerated.

A pitch angle (not shown) of rotor blades 112, i.e., an angle thatdetermines the perspective of rotor blade 112 with respect to thedirection of wind 114, may be changed by a pitch assembly (not shown inFIG. 1). More specifically, increasing a pitch angle of rotor blade 112decreases an amount of rotor blade surface area 126 exposed to wind 114and, conversely, decreasing a pitch angle of rotor blade 112 increasesan amount of rotor blade surface area 126 exposed to wind 114. The pitchangles of rotor blades 112 are adjusted about a pitch axis 128 at eachrotor blade 112. In the exemplary embodiment, the pitch angles of rotorblades 112 are controlled individually. Further, wind turbine 100includes a main gearbox 130 and a generator 200 within nacelle 106. Inthe exemplary embodiment, main shaft assembly 108 includes a low-speedshaft (not shown in FIG. 1) that extends into main gearbox 130 and ahigh-speed shaft (not shown in FIG. 1) extends to generator 200.

FIG. 2 illustrates a schematic view of generator 200. Generator 200includes a stator 210 and rotor 212. The generator input shaft 220 iscoupled to the gearbox output shaft 225 via a coupling 221. Typically,coupling 221 is a bolted flange configuration. The generator input shaft220 is located at the drive end (DE) 214 of the generator. The opposingend of the generator 200 is the non-drive end (NDE) 216. The non-driveend 216 includes a bearing shield 230. The bearing shield 230 may alsoinclude an inner bearing cover 231, and the outside of the bearingshield 230 may be configured for attachment of an oil slinger 232, and aslip ring housing 233 containing slip rings 234.

FIG. 3 illustrates a perspective view of the non-drive end 216 ofgenerator 200. The bearing shield 230 is shown attached to the generator200, however the slip ring housing 233, slip rings 234 and other partshave been removed. It can be seen that the existing bearing shield is asolid cover (except for the portion that the rotor shaft passesthrough).

FIG. 4 illustrates a perspective view of the non-drive end 216 ofgenerator 200 with the bearing shield 230 removed. A generator rotor fan440 is attached to the rotor and is configured as a radial flow fan.However, the rotor fan 440 could also be an axial flow type fan as well.Access to the rotor fan is important during a rebalancing operation, aswill be described in more detail hereinafter.

FIG. 5 illustrates a perspective view of the non-drive end 216 ofgenerator 200 with the rotor fan 440 removed. The rotor's end windings513 extend circumferentially around the rotor. The end-windings 513 areconnected to a Wye-ring 514 that is fit radially inside the end windings513. The Wye ring 514 is typically one or more copper bars curved into agenerally circular shape, and the Wye ring 514 provides a floatingneutral connection for the (typically) three phases of the rotorwindings. The Wye-ring 514 is normally insulated by wrapping and/orencapsulating in dielectric material.

As stated previously, operational wear and tear can cause cracks in theWye-ring 514. If two or more cracks develop, the generator malfunctionsand must be shut down. FIG. 6 illustrates a schematic view of the rotorend windings 513 connected to the Wye ring 514. Connection lugs 651, 652and 653 are used to electrically connect the Wye ring 514 to the endwindings 513. Typically, the connection lugs are brazed to the Wye ring514 as both are made of copper. The brazed joint experiences strainduring operation of the generator. For example, thermal expansion andcontraction may not be uniform between the rotor end windings 513 andthe Wye ring 514, and this uneven expansion and contraction stresses thebrazed joint as well as the Wye ring itself. Unfortunately, after anextended period of time a crack 661 may form in the Wye ring nearconnection lug 651. A single crack is not catastrophic, as current canstill flow to the nearby connection point. However, crack 661 doesimpose additional loads on the other two connection lugs 652 and 653. Ifa second crack 662 develops near connection lug 662, one of the phases(via connection lug 651) is now isolated from the floating neutral.Arcing between the cracks will degrade the insulation and will triggermachine faults.

FIG. 7 illustrates a schematic view of the rotor 212 after a replacementWye ring 714 has been installed. In the past, there was no way to repaira cracked (or otherwise malfunctioning) Wye ring 514 up-tower, orin-situ. The entire old generator had to be removed and a new generatorwas brought up to the nacelle and installed. As one might expect, thiswas a very expensive and time consuming operation, but the only knownway to fix the generator. According to an aspect of the presentinvention, a new (or replacement) Wye ring 714 is installed and placedradially inside the old Wye ring 514.

To expose the connection lugs 651-653, the existing insulation must beremoved from portions of the old Wye ring 514. The replacement Wye ring714 will be fastened to the connection lugs. The fastening system mayinclude a bolt 771, anti-rotation nut 772 and one or more shims 773. Thereplacement Wye ring 714 may be made of copper or aluminum, and ofsufficient diameter to nest just inside (but not in direct contact with)the previous Wye ring 514. The fastening system may also include platedsurfaces (e.g., silver plated) to increase conductivity. Afterinstallation of the replacement Wye ring 714, the connection lugs651-653, old exposed Wye ring 514 portions and new Wye ring 714 (as wellas the fastening system) are encapsulated in dielectric (or insulating)material.

The installation of this new hardware creates an imbalance problem forthe rotor 212. It is highly likely that the rotor 212 will now be out ofbalance due to the addition of this new hardware, and some rotors haveasymmetrically located connection lugs which further exacerbates therotor balance problem. New generators built in a factory do not havethis problem, as they are balanced during the building process. However,such a modification of a generator rotor in the field will almostinvariably cause some rotor imbalance. As only the non-drive end 216 wasmodified, only the non-drive end 216 will most likely need to bebalanced to bring the generator back into an acceptable balancedcondition. The type of balancing performed on new generators is calledtwo-plane balancing, since there are two bearing points at aconsiderable distance involved. The method, according to aspects of thepresent invention, will result in a dynamic balancing which will comeclose to the factory balancing but a residual and acceptable unbalancemay remain. This could only be dealt with by performing a completetwo-plane balancing, and to accomplish this the drive end 214 bearingshield (not shown) would have to be removed and replaced with atemporary one as shown in FIGS. 8 and 9. Typically, the factory (whenbuilding new generators) does not balance the rotor 212 with theslip-rings 234 or the entire slip ring assembly attached to the rotor212. Therefore, the slip rings (or slip ring assembly) may be left offof the rotor during an in-situ rebalancing operation, if desired inspecific applications. However, during a rebalancing operation it may bedesirable to have other rotor attachments (e.g., the inner bearingcover, oil slinger, etc.) in place an attached to the rotor or rotorshaft. A system and method to accomplish such an in-situ (and up-tower)rotor rebalancing will now be described.

FIG. 8 illustrates a perspective front view of a bearing shield 800,according to an aspect of the present invention. The bearing shield 800is a temporary bearing shield that is installed on the generator 200 andmimics the original bearing shield 230 dimensionally in such a way thatall rotating parts of the rotor can be mounted as they are in a normaloperating condition. The rotating parts may include the oil slinger,slip-ring or any other rotating part of the rotor that will affectbalance thereof.

The temporary bearing shield 800 includes a first half 801 joined to asecond half 802 by a nut 811 and bolt 812 arrangement. The two halves801, 802 could also be joined by any other suitable joining method. Thetemporary bearing shield 800 includes a central aperture for supportinga non-drive portion of the rotor shaft to pass through. A plurality ofwindows 804, 805, 806, 807 are configured to permit operator access tothe generator rotor fan 440, so that balancing weights may be attachedthereto. The fan 440 is a good candidate for weight attachment as itprovides many points with good surface area for weight attachment. Thetemporary bearing shield 800 also includes mounting means for mountingthe NDE non-rotating parts of the generator rotor, and these mountingmeans may include threaded holes 821, 822, 823, 824 or other suitablebrackets or hangers as provided on the original bearing shield 230.Non-rotating parts may include the inner bearing cover, inner bearingcap or other non-rotating parts.

FIG. 9 illustrates a perspective back view of the temporary bearingshield 800, according to an aspect of the present invention. Thetemporary bearing shield 800 includes a plurality of through holes901-908 and for bolt passage and mounting of the shield 800 on thenon-drive end 216 of generator 200. Through holes 821-824 may be used toattach the inner bearing cover 231 to the temporary bearing shield 800.During a rebalancing operation, the state of balance must be detected sothe temporary bearing shield 800 also includes an accelerometer 910 thatis configured to detect the state of rotor balance or imbalance.Accelerometer 910 may be a single axis type of accelerometer and can bemagnetically attached to mount 915. The single axis type ofaccelerometer is preferably oriented radially towards the center ofgyration to pick up the vibrations created by an unbalanced rotorcondition. One accelerometer is shown, but it is to be understoodmultiple accelerometers could be used during a rotor rebalancingoperation. As one example only, one accelerometer could be placed on thenon-drive end 216 and another accelerometer could be placed on the driveend 214.

FIG. 10 illustrates a perspective view of a pony motor assembly 1000,according to an aspect of the present invention. The pony motor assembly1000 is configured for attachment to the drive end 214 of generator 200,and is also configured to rotate the generator rotor input shaft 220during a rebalancing operation. The pony motor assembly 1000 includes amotor 1010 contained within motor housing 1012. The motor housing 1012is attached to the generator 200 by a pony motor mount. The pony motormount includes two brackets 1020, 1022 and a bracket mount 1024. Thebrackets 1020, 1022 are configured to be attached to generator 200 viabracket mount 1024. The motor 1010 drives a drive pulley 1014 thatrotates a belt 1116 connected to the rotor input shaft 220. To providetension for belt 116 a turnbuckle rod 1030 is configured for attachingthe pony motor assembly 1000 to the generator 200. The turnbuckle rod1030 may be attached to bolt 1032 threaded into generator 200, or anyother suitable mounting location on the generator or other supportingstructure. The turnbuckle rod 1030 can be rotated to increase ordecrease tension on belt 1116.

The generator rotor 212 is very heavy (e.g., about 2 metric tons), andhas its mass concentrated around a fairly large radius. This results ina very large inertia which needs to be overcome. If one were to employ amotor that would be started ‘across the lines’, that is by switching iton, the belt(s) might break or slip and burn up before the rotor 212would come up to speed. A ‘soft-start’ motor controller would be verybulky and heavy plus the motor that goes along with such a controllerwould also be bulky and heavy, which makes for a difficult tasktransporting the motor and controller up the tower. As a more preferableoption, a servo-drive motor 1010 is used which is controlled via acomputer. A servo-drive motor can be started with tremendous torque atvery low rpm and accelerated in a controlled way. For example, the motor110 can have a very small speed increase rate in order to get the rotor212 moving without slipping the belt 1116 or overloading the driveelements or motor 1010.

FIG. 11 illustrates a perspective view of the pony motor assembly 1000connected to the generator rotor input shaft, according to an aspect ofthe present invention. The pulley 1118 may be connected to the rotorinput shaft 220 via any suitable mounting means (e.g., a bolted flangeconnection, etc.). To rotate the generator rotor 212, the motor isenergized to rotate the drive pulley 1014, this in turn drives belt 1116that rotates pulley 1116 and rotor input shaft 220. As one example only,motor 1010 may drive rotor 212 at about 200 rpm to about 400 rpm duringa rebalancing operation.

FIG. 12 illustrates a flow chart of a method 1200 for balancing (orrebalancing) a generator rotor 212 in-situ. This method can be performedwhile the generator 200 is located inside of a nacelle 106 on top of awind turbine tower 102. The method includes a step 1210 of attaching atemporary bearing shield 800 to a non-drive end 216 of a generator 200.This step may also include attaching rotating parts of the generatorrotor to the generator rotor and attaching non-rotating parts to thetemporary bearing shield. An attaching step 1220 attaches a pony motorassembly 1000 to a drive-end 214 of the generator 200. A connecting step1230 connects the pony motor assembly 1000 to the generator rotor inputshaft 220 (and therefore rotor 212). This step may also includeattaching a pulley 1118 to the rotor 212 (or input shaft 220) andconnecting the pulley 1118 to the pony motor assembly 1000 via belt1116. The belt can be tensioned by attaching a turnbuckle rod 1030 tothe generator and the pony motor assembly 1000. The turnbuckle rod canbe rotated to increase or decrease the length thereof, and therebyincreasing or decreasing the amount of tension on belt 1118. To test thebalance of the rotor and activating step 1240 activates the pony motorassembly (i.e., motor 1010) to rotate the generator rotor 212, and adetecting step 1250 detects a condition of generator rotor balance orimbalance. The detecting step 1250 may also include receiving data fromone or more accelerometers (e.g., accelerometer 910) that output dataused to indicate the condition of the rotor balance/imbalance. A weightaddition step 1260 adds weight to the generator rotor 212 if a rotorimbalance condition is detected to correct the rotor imbalance. Theweight addition step may include adding weight to specific portions offan 440 (or other parts of rotor 212) to correct rotor balance.

FIG. 13 illustrates a schematic view of the system for rebalancing thegenerator rotor while the generator 200 is within wind turbine 100. Thesystem includes temporary bearing shield 800, pony motor assembly 1100,both of which are shown attached to generator 200, and computer 1300.The rebalancing system 1310 of the invention can be implemented insoftware (e.g., firmware), hardware, or a combination thereof. In thecurrently contemplated best mode, the rebalancing system 1310 isimplemented in software, as an executable program, and is executed by aspecial or general purpose digital computer, such as a personal computer(PC; IBM-compatible, Apple-compatible, or otherwise), workstation,minicomputer, or mainframe computer. An example of a general purposecomputer that can implement the rebalancing system 1310 of the presentinvention is shown in FIG. 13.

Generally, in terms of hardware architecture, as shown in FIG. 13, thecomputer 1300 includes a processor 1312, memory 1314, and one or moreinput and/or output (I/O) devices 1316 (or peripherals) that arecommunicatively coupled via a local interface 1318. The local interface1318 can be, for example but not limited to, one or more buses or otherwired or wireless connections, as is known in the art. The localinterface 1318 may have additional elements, which are omitted forsimplicity, such as controllers, buffers (caches), drivers, repeaters,and receivers, to enable communications. Further, the local interfacemay include address, control, and/or data connections to enableappropriate communications among the aforementioned components.

The processor 1312 is a hardware device for executing software,particularly that stored in memory 1314. The processor 1312 can be anycustom made or commercially available processor, a central processingunit (CPU), an auxiliary processor among several processors associatedwith the computer 1300, a semiconductor based microprocessor (in theform of a microchip or chip set), a macroprocessor, or generally anydevice for executing software instructions. Examples of suitablecommercially available microprocessors are as follows: a PA-RISC seriesmicroprocessor from Hewlett-Packard Company, an 80×86 or Pentium seriesmicroprocessor from Intel Corporation, a PowerPC microprocessor fromIBM, a Sparc microprocessor from Sun Microsystems, Inc, or a 68xxxseries microprocessor from Motorola Corporation.

The memory 1314 can include any one or combination of volatile memoryelements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM,etc.)) and nonvolatile memory elements (e.g., ROM, hard drive, tape,CDROM, etc.). Moreover, the memory 1314 may incorporate electronic,magnetic, optical, and/or other types of storage media. Note that thememory 1314 can have a distributed architecture, where variouscomponents are situated remote from one another, but can be accessed bythe processor 12.

The software in memory 1314 may include one or more separate programs,each of which comprises an ordered listing of executable instructionsfor implementing logical functions. In the example of FIG. 1, thesoftware in the memory 1314 includes the rebalancing system 1310 inaccordance with the present invention and a suitable operating system(O/S) 1322. A nonexhaustive list of examples of suitable commerciallyavailable operating systems 1322 is as follows: (a) a Windows operatingsystem available from Microsoft Corporation; (b) a Netware operatingsystem available from Novell, Inc.; (c) a Macintosh operating systemavailable from Apple Computer, Inc.; (e) a UNIX operating system, whichis available for purchase from many vendors, such as the Hewlett-PackardCompany, Sun Microsystems, Inc., and AT&T Corporation; (d) a LINUXoperating system, which is freeware that is readily available on theInternet; (e) a run time Vxworks operating system from WindRiverSystems, Inc.; or (f) an appliance-based operating system, such as thatimplemented in handheld computers or personal data assistants (PDAs)(e.g., PalmOS available from Palm Computing, Inc., and Windows CEavailable from Microsoft Corporation). The operating system 1322essentially controls the execution of other computer programs, such asthe rebalancing system 1310, and provides scheduling, input-outputcontrol, file and data management, memory management, and communicationcontrol and related services.

The rebalancing system 1310 is a source program, executable program(object code), script, or any other entity comprising a set ofinstructions to be performed. When a source program, then the programneeds to be translated via a compiler, assembler, interpreter, or thelike, which may or may not be included within the memory 1314, so as tooperate properly in connection with the O/S 1322. Furthermore, therebalancing system 1310 can be written as (a) an object orientedprogramming language, which has classes of data and methods, or (b) aprocedure programming language, which has routines, subroutines, and/orfunctions, for example but not limited to, C, C++, Pascal, Basic,Fortran, Cobol, Perl, Java, and Ada. In the currently contemplated bestmode of practicing the invention, the rebalancing system 1310 isconnected to the accelerometers 911-914 and data received from theaccelerometers is used to indicate the state of balance/imbalance ofrotor 212 and if the rotor is imbalanced, then where to place balancingweights and how much weight to place at each designated location onrotor 212 (or fan 440 or any other suitable rotor location).

The I/O devices 1316 may include input devices, for example but notlimited to, an accelerometers 910, a keyboard, mouse, scanner,microphone, etc. Furthermore, the I/O devices 1316 may also includeoutput devices, for example but not limited to, a printer, display, etc.Finally, the I/O devices 1316 may further include devices thatcommunicate both inputs and outputs, for instance but not limited to, amodulator/demodulator (modem; for accessing another device, system, ornetwork), a radio frequency (RF) or other transceiver, a telephonicinterface, a bridge, a router, etc.

If the computer 1300 is a PC, workstation, laptop, smartphone, tablet orthe like, the software in the memory 1314 may further include a basicinput output system (BIOS) (omitted for simplicity). The BIOS is a setof essential software routines that initialize and test hardware atstartup, start the O/S 1322, and support the transfer of data among thehardware devices. The BIOS is stored in ROM so that the BIOS can beexecuted when the computer 1300 is activated. When the computer 1300 isin operation, the processor 1312 is configured to execute softwarestored within the memory 1314, to communicate data to and from thememory 1314, and to generally control operations of the computer 1300pursuant to the software. The rebalancing system 1310 and the O/S 1322,in whole or in part, but typically the latter, are read by the processor1312, perhaps buffered within the processor 1312, and then executed.

When the rebalancing system 1310 is implemented in software, as is shownin FIG. 31, it should be noted that the rebalancing system 1310 can bestored on any computer readable medium for use by or in connection withany computer related system or method. In the context of this document,a computer readable medium is an electronic, magnetic, optical, or otherphysical device or means that can contain or store a computer programfor use by or in connection with a computer related system or method.The rebalancing system 1310 can be embodied in any computer-readablemedium for use by or in connection with an instruction execution system,apparatus, or device, such as a computer-based system,processor-containing system, or other system that can fetch theinstructions from the instruction execution system, apparatus, or deviceand execute the instructions. In the context of this document, a“computer-readable medium” can be any means that can store, communicate,propagate, or transport the program for use by or in connection with theinstruction execution system, apparatus, or device. The computerreadable medium can be, for example but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, device, or propagation medium. More specific examples (anonexhaustive list) of the computer-readable medium would include thefollowing: an electrical connection (electronic) having one or morewires, a portable computer diskette (magnetic), a random access memory(RAM) (electronic), a read-only memory (ROM) (electronic), an erasableprogrammable read-only memory (EPROM, EEPROM, or Flash memory)(electronic), an optical fiber (optical), and a portable compact discread-only memory (CDROM) (optical). Note that the computer-readablemedium could even be paper or another suitable medium upon which theprogram is printed, as the program can be electronically captured, viafor instance optical scanning of the paper or other medium, thencompiled, interpreted or otherwise processed in a suitable manner ifnecessary, and then stored in a computer memory.

In an alternative embodiment, where the rebalancing system 1310 isimplemented in hardware, the rebalancing system 1310 can implementedwith any or a combination of the following technologies, which are eachwell known in the art: a discrete logic circuit(s) having logic gatesfor implementing logic functions upon data signals, an applicationspecific integrated circuit (ASIC) having appropriate combinationallogic gates, a programmable gate array(s) (PGA), a field programmablegate array (FPGA), etc.

FIG. 14 illustrates a flow chart of a method 1400 for repairing (orservicing) a rotor 212 of a generator 200 in a wind turbine 100. Themethod 1400 may be performed in-situ, or while the generator 200 ishoused within the nacelle 106 of the wind turbine 100. The method 1400includes a step 1410 of dismantling a non-drive end 216 of the generator200. See also FIGS. 3-5. This step may also include dismantling thenon-drive end 216 to expose the rotor 212, existing Wye ring 514 andexisting connection lugs 651, 652, 653. Step 1420 removes insulationfrom portions of the existing Wye ring 514 and the existing connectionlugs 651, 652, 653. This step may also include removing blocking andsupport material from portions of the existing Wye ring 514 and theexisting connection lugs 651, 652, 653. Step 1430 removes portions ofthe existing Wye ring 514 near the existing connection lugs 651, 652,653. This step may also include electrically disconnecting the existingWye ring 514 from the rotor 212 or rotor end windings 513.

Step 1440 installs the replacement Wye ring 714 in the generator 200.See FIG. 7. This step may also include positioning the replacement Wyering 714 radially inside the existing Wye ring 514 and co-axial with therotor 212 or central shaft of the rotor. Step 1450 connects thereplacement Wye ring to the existing connection lugs 651, 652, 653. Thisstep may include drilling a through hole 1570 into each of the existingconnection lugs and mechanically fastening the replacement Wye ring 714to each of the existing connection lugs with a bolt 771, a nut 772(which may be an anti-rotation nut) and one or more shims 773. FIG. 15is an exploded and perspective view of the connection arrangement usedto connect the replacement Wye ring 714 to the connection lug 651. Nut772 includes an overhang 1580 used to prevent the nut 772 from turningwhen placed on the connection lug 651.

Step 1460 insulates the replacement Wye ring 714 and the existingconnection lugs 651, 652, 653. Method 1400 may also include the steps ofpartially reassembling the generator, attaching a temporary bearingshield to the non-drive end of the generator, detecting a condition ofrotor balance or imbalance, and adding weight to the rotor if a rotorimbalance condition is detected to correct the rotor imbalance.

The method and system of the present invention demonstratessubstantially improved results that were unexpected, because a generatorhaving a defective Wye ring can now be repaired in-situ and up-tower ina wind turbine. Previously, the only known solution was to remove theentire generator and install a new generator (a costly and timeconsuming endeavor). The method and system of the present inventionenables the wind turbine to be restored to operating condition muchfaster and at much less expense.

The method and system of the present invention demonstratessubstantially improved results that were unexpected, because a generatorhaving a defective Wye ring can now be repaired in-situ and up-tower ina wind turbine. Previously, the only known solution was to remove theentire generator and install a new generator (a costly and timeconsuming endeavor). The method and system of the present inventionenables the wind turbine to be restored to operating condition muchfaster and at much less expense.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

The invention claimed is:
 1. A system for rebalancing a generator rotor,the system comprising: a temporary bearing shield configured to supporta non-drive end of the generator rotor; a pony motor assembly configuredfor attachment to a drive end of the generator rotor, the pony motorassembly configured to rotate the generator rotor during a rebalancingoperation; and wherein the temporary bearing shield and the pony motorassembly enable the generator rotor to be rotated during an in-siturebalancing operation.
 2. The system of claim 1, the temporary bearingshield further comprising: an accelerometer configured to detectgenerator rotor imbalance.
 3. The system of claim 1, the temporarybearing shield further comprising: a plurality of windows configured topermit access to a generator rotor fan, and so that balancing weightsmay be attached to the generator rotor fan.
 4. The system of claim 1,the temporary bearing shield further comprising: mounting means formounting non-rotating parts of the generator rotor.
 5. The system ofclaim 4, wherein the non-rotating parts include an inner bearing cover.6. The system of claim 1, the pony motor assembly further comprising: amotor; a pulley configured for attachment to the drive end of thegenerator rotor; a belt connecting the motor and the pulley.
 7. Thesystem of claim 6, the pony motor assembly further comprising: a ponymotor mount configured for attaching the pony motor assembly to agenerator.
 8. The system of claim 7, the pony motor assembly furthercomprising: a turnbuckle rod configured for attaching the pony motorassembly to the generator, the turnbuckle rod also configured to providetension to the belt.
 9. The system of claim 6, the motor comprising aservo-drive motor.
 10. A system for rebalancing a generator rotor, thesystem comprising: a temporary bearing shield configured to support anon-drive end of the generator rotor, the temporary bearing shieldfurther comprising a plurality of windows configured to permit access toa generator rotor fan, and so that balancing weights may be attached tothe generator rotor fan, and an accelerometer configured to detectgenerator rotor imbalance; a pony motor assembly configured forattachment to a drive end of the generator rotor, the pony motorassembly configured to rotate the generator rotor during a rebalancingoperation; and wherein the temporary bearing shield and the pony motorassembly enable the generator rotor to be rotated during an in-siturebalancing operation.
 11. The system of claim 10, the pony motorassembly further comprising: a servo-drive motor; a pulley configuredfor attachment to the drive end of the generator rotor; a beltconnecting the servo-drive motor and the pulley; a pony motor mountconfigured for attaching the pony motor assembly to a generator; and aturnbuckle rod configured for attaching the pony motor assembly to thegenerator, the turnbuckle rod also configured to provide tension to thebelt.
 12. The system of claim 11, the temporary bearing shield furthercomprising: mounting means for mounting non-rotating parts of thegenerator rotor; and wherein the non-rotating parts include an innerbearing cover.
 13. A method for rebalancing a generator rotor, themethod comprising the steps of: attaching a temporary bearing shield toa non-drive end of a generator; attaching a pony motor assembly to adrive-end of the generator; connecting the pony motor assembly to thegenerator rotor; activating the pony motor assembly to rotate thegenerator rotor; detecting a condition of generator rotor balance orimbalance; adding weight to the generator rotor if a rotor imbalancecondition is detected to correct the rotor imbalance; wherein, themethod is performed on the generator in-situ.
 14. The method of claim13, wherein the generator is located in the nacelle of a wind turbine.15. The method of claim 14, the attaching a temporary bearing shieldstep further comprising at least one of: attaching rotating parts of thegenerator rotor to the generator rotor; attaching non-rotating parts tothe temporary bearing shield.
 16. The method of claim 14, the connectingthe pony motor assembly step further comprising: attaching a pulley tothe generator rotor and connecting the pulley to the pony motor assemblyvia a belt.
 17. The method of claim 16, the connecting the pony motorassembly step further comprising: attaching a turnbuckle rod to thegenerator and the pony motor assembly; providing tension to the belt byrotating the turnbuckle rod.
 18. The method of claim 14, the detecting acondition of generator rotor balance or imbalance step furthercomprising: receiving data from an accelerometer, the data indicatingthe condition of generator rotor balance or imbalance.
 19. The method ofclaim 14, the adding weight step further comprising: adding weight to arotor fan to correct generator rotor imbalance.
 20. The method of claim13, wherein the pony motor assembly comprises a servo-drive motor.